Polycrystalline diamond (PCD) materials known in the art are formed from diamond grains or crystals and a ductile metal binder and are synthesized by high temperature/high pressure processes. Such material is well known for its mechanical properties of wear resistance, making it a popular material choice for use in such industrial applications as cutting tools for machining, and subterranean mining and drilling where such mechanical properties are highly desired. For example, conventional PCD can be provided in the form of surface coatings on, e.g., cutting elements used with cutting and drilling tools to impart improved wear resistance thereto.
Generally, PCD-containing cutting elements used in such applications are formed by coating a carbide substrate with a layer of PCD. Such cutting elements include a substrate, a surface layer, and often a transition layer to improve the bonding between the exposed layer and the substrate. The substrate is generally a carbide material, e.g., cemented carbide, tungsten carbide (WC) cemented with cobalt (WC—Co).
The PCD layer generally includes metal binder up to about 30 percent by weight. The metal binder facilitates diamond intercrystalline bonding, and bonding of diamond layer to the substrate. Metals employed as the binder are often selected from cobalt, iron, or nickel and/or mixtures or alloys thereof and may include metals such as manganese, tantalum, chromium and/or mixtures or alloys thereof. However, while higher metal binder content generally increases the toughness of the resulting PCD material, higher metal content also decreases the PCD material hardness and wear resistance, thus limiting the flexibility of being able to provide PCD coatings having desired levels of hardness, wear resistance and toughness. Additionally, when variables are selected to increase the hardness or wear resistance of the PCD material, generally brittleness also increases, thereby reducing the toughness of the PCD material.
Conventional PCD cutting elements may optionally include one or more transition layers between the PCD layer and the substrate. Such transition layers may include refractory particles such as carbides in addition to the diamond and metal binder to change material properties through the layers. However, carbide content manipulation does not necessarily promote the best transition between adjacent PCD layers, permitting discrete interfaces to exist between the layers which can promote unwanted stress concentrations. The existence of these discrete interfaces, and the resulting stress concentrations produced therefrom, can cause premature failure of the PCD cutting element by delamination along the layer-to-layer interfaces.